Producing plasticizers from coal tar



Patented 'July 28, 1942 UiTED STATES PATENT Jacquelin E. Harvey, Jr., Atlanta, Ga., assignor of one-half to Southern Wood Preserving Company, East Point, Ga., a corporation of Georgia No Drawing. Application July 13, 1940, Serial No. 345,436

1 Claim.

The present invention relates to the production of solvents from tars and fractions thereof of aromatic content.

An object of the present invention is the conversion of tars and/or fractions thereof of aromatic content into solvents and/or plasticizers.

Another object of the present invention is the conversion of mixtures of tar fractions, while under influence of a catalyst, said catalyst having at least partial sulfide content, into solvents and/or plasticizers.

Yet another object of the present invention is the substantially total conversion of a mixture of tar fractions, by aid of catalysts, into solvents and/or plasticizers, said conversion characterized by provision of conditions that maintain said catalysis at substantially optimum conditions.

Other objects of the present invention will become apparent from the following disclosures.

Usable starting materials of the present process include tars or fractions thereof, characterized by aromatic content. Said tars include destructive distillation products of coal, as for instance, high temperature coke oven tar, low temperature tar and gas house tar; aromatic extracts of coal and petroleum; high boiling aromatic hydrocarbons produced by polymerization of petroleum or fractions thereof, including gas and gases.

The present process provides a method for the conversion of tar and/or fractions thereof, said tar and fractions thereof being characterized by the presence of a multiplicity of rings, into solvents and/or plasticizers of superior aromaticity.

By the terms multiplicity of rings, ring mul tiples, or molecular complexes are meant those high boiling fractions, including pitch or tar fractions of aromatic content that may be viewed as having little or no solvency or plasticity when compared to conventional low boiling solvents or commercial plasticizers.

The molecular complexes necessitate step-Wise treatment for conversion to the solvents and/or plasticizers of the present invention. By the term step-wise is meant that when converting substantially the entirety of starting material into the solvents and/or plasticizers of the present invention, said conversion is not effected in entirety by merely once impressing on the starting material the control variables of the present process, but rather by repeatedly impressing the process controls, as hereinafter stated, on said starting material. The unconverted portion approaches zero as representing a maximum conversion; that is to say, the process controls of the present process are impressed on the starting material for conversion of a percentage, but less than the whole, into solvents and/ or plasticizers; after removal of said induced solvents and/or plasticizers by known methods, the unconverted portion, with or without addition of starting material to compensate for product recovery, is again subjected to process controls for induction of said products, etc.

Viewed broadly, the present invention provides a process wherein the starting materials are subjected to the action of hydrogen, under catalyzed conditions characterized by said catalysis being maintained at optimum conditions by specific provision, whereby to convert said starting material in aforesaid step-Wise manner into solvents and/or plasticizers. The process of the present invention is further characterized by be ing practiced in the liquid phase, as opposed to vapor phase that vaporizes substantially the entirety of the feed stock. The term liquid phase may not be technically correct, inasmuch as Varying amounts of the starting feed are vaporized; however, there is a definite line of demarcation between the liquid phase herein used and the commonly accepted vapor phase.

Among other things, the liquid phase hydrogenation of the present process is employed for the following reasons, viz: that the solvents of the present invention are thereby made more aromatic than solvents produced in true vapor phase hydrogenation and that maintenance of liquid phase makes possible continued step-wise conversion to the end that substantially volume for volume conversion be effected.

The following examples will serve to illustrate modes of practicing the process of the present invention.

Example 1.A coal tar fraction boiling substantially 3% at 380 C. was passed through a high pressure reaction vessel while contacting a sulphide catalyst and while simultaneously flowing hydrogen therethrough, at a pressure of 300 atmospheres and a temperature of 410 (3.; time of reaction one and one half hours. The beneficiated material was found to have an initial boiling point of substantially C. and was distilled to an upper limit of 200 C. to recover the distillate as a solvent of superior quality, that is to say, a solvent of substantially 50% aromatic content, or more. The residue resulting from said distillation was fed back to the reaction vessel with crude starting material.

At the end of the 36th hour of operation the synthesis of the solvent had declined. Research disclosed that the reason therefor was apparent conversion of the sulphide catalyst into other form. Identical operations were repeated using the same starting material, except that the feed was adjusted to contain one half of one percent sulphur. On the repeating operations the percentage of solvent increment held constant, other than loss normally anticipated due to catalyst age. The beneficiated feed stock being stripped up to 200 C, for said solvent recovery and the residue therefrom being recycled to the end that substantially volume for Volume of the starting material be converted, neglecting normal manufacturing loss, to the solvent specified.

Thus the present example illustrates a process for converting in step-wise manner, a mixture of tar fractions substantially in their entirety, into solvents of superior quality, characterized by said conversion being effected in liquid phase, and further characterized by maintenance, without substantial reduction, of original conversion ratio other than changes due to straightening-out or ageing of said sulphide catalyst.

Concerning the addition of sulphur to the feed stock, the sulphur content of the starting material, including recycle material, is adjusted to that sulphur content which will provide maintenance of the catalyst in substantial sulphide form. Thus, forming an important part of the present invention is the maintenance of a hydrogen sulphide partial pressure of at least a fractional atmosphere, or as high as one atmosphere, or higher. A few trials will readily disclose that hydrogen sulfide partial pressure that will maintain the catalyst in substantial sulphide form under given conditions.

Of course, the sulphur may be supplied in forms other than elemental sulphur. Sulphur may be added in any form capable of generating hydrogen sulphide to the end that the catalyst be maintained in substantial sulphide form.

Some tars, or fractions thereof, including aromatic extracts of petroleum or petroleum fractions and polymerization products thereof, may have suflicient sulphur, or sulphur compound therein to obviate the necessity of sulphur addition.

Thus, it will be seen that the invention provides a process for the conversion, substantially in entirety, of a mixture of tar fractions into solvents of superior quality, said conversion being characterized by subjecting the starting material in liquid phase to the action of hydrogen and hydrogen sulphide, said hydrogen sulphide representing a partial pressure of at least a fractional atmosphere; said conversion being further characterized by the presence of a sulphide catalyst maintained in substantial sulphide form, the while catalyzing step-wise reduction to substantially total conversion of the starting material as aforesaid.

Eacamlple 2.-Coa1 tar pitch boiling substantially 15% at 355 C. is passed through a high pressure reactor, while simultaneously flowing hydrogen therewith; catalyst, molybdenum sulphide; pressure 300 atmospheres and temperature 400 (3.; hydrogen sulphide partial pressure 1 atmosphere and gas flow in excess of 4,000 cubic feet per barrel feed; reaction time 1 hour. The beneficiated material after being relieved of its dissolved and occluded gas was returned to the reaction system and treated under identical conditions, except the temperature was raised to 425 C. The twice beneficiated material was distilled to an upper limit of 290 C. to recover the solvent which had an overall aromaticity of more than 50% and distilled predominantly between 150 C. and 282 C. The solvent so produced may be fractionally cut to provide solvents of varied boiling ranges.

After the starting material has been subjected to the process controls for solvent production, the point at which the fractional cut is made for solvent recovery is not an inflexible point, but is rather varied by desired end point of the recovered solvent. In the following tabular data are shown end points of various commercial solvents, substitutes for which may be provided by the solvents of the present process.

Solvents Identification: End point, C. Benzol Toluol Hi-flash naphtha 200 Heavy naphtha 290 High boiling crudes and plasticizers 360 or, other end points may be provided.

When recovering the solvents of the present invention from the beneficial material, as for instance, when recovering the solvent to an upper limit of 360 C., the fractional part boiling between (as an example) 300 C. and 360 C. may be used as a plasticizing oil, or the like.

Example 3.Coal tar, boiling predominantly above C. was subjected to the action of hydrogen and hydrogen sulphide at 400 C. for one half hour; catalyst molybdenum and tin sulphide; pressure 400 atmospheres and hydrogen sulphide partial pressure substantially 1%; atmospheres. The beneficiated material was then subjected to a second treatment under identical conditions, except that the temperature was raised to 450 C. and treatment continued for 1 hour. The beneficiated mass was then distilled to an upper limit of 290 C. to recover the solvent as a distillate. The residue therefrom was added to fresh starting tar and recycled; sulphur content being adjusted. The solvent afterwards recovered had an aromaticity of greater than 50%.

The liquid phase of the present invention, as heretofore explained, is used for the reason that only in liquid phase can step-wise reduction of substantially the entirety of the starting material be effected to solvents of superior solvency.

Continuous or batch methods may be used. In the eventcontinuous conversion is practiced, conversion may be effected in a single reactor, a series of reactors, a parallelism of reactors, including a multiplicity thereof. When practicing continuous methods wherein hydrogen or hydrogen-containing gas flows in a stream, varying amounts of said gas may be used, dependent upon results desired. However, the fiow of gas is always held, at least, slightly in excess of that amount which induces appreciable carbonaceous increment, which increment is, however, not to be confused with that carbonaceous increment that is inherent to the process and which usually causes plant shut-down, as an example, every 3 to 6 or 9 months, or longer. The gas flow, using average tars, or fractions thereof, is desirably held in excess of 3,000 cubic feet per barrel material treated.

By the term beneficiated as used herein and in the appended claims is meant starting material at least once subjected to the action of hydrogen.

Tar, or fractions thereof, that have had their carbon content lowered are especially adapted to be used as starting materials of the present process, and the claims are to be read with this disclosure in mind. The terms tar and tar fractions as used herein and in the appended claims are meant to cover said tar and/or tar fractions up to substantially the time of actual conversion into solvents of the present invention.

The time element cannot be stated as a definite figure because of varying grades of the starting material, and the low end of the solvents desired. For instance, solvents boiling as low as commercial benzol, or lower, may be produced.

The process variables are adapted to various coordinations to produce low boiling solvents and/or high boiling solvents. Excessive time element may be substituted for increased temperatures in some cases when producing additional solvent increment and/or lower boiling ends.

As is well known, hydrogenations proceed at moderate temperatures and pressures; however, to approximate commercial necessities, elevated temperatures and pressures are desirable. Temperatures as low as 250 C. and pressures as low as 50 atmospheres are usable; however, with catalysts now commercially available, the necessity of inordinately long periods of treatment makes higher temperatures and pressures desirable. With pressures of 200 atmospheres and above, and temperatures of 375 C. and above, when converting as aforenamed in said catalyzed manner, good results have been obtained.

Catalysts assist in speeding and directing the desired reaction of the process of the present invention. All hydrogenating catalysts of sulphide form are usable. However, catalysts other than of sulphide form may be provided, with subsequent conversion to the sulphide or partially sulphide form due to the action of supplied hydrogen sulphide. Various catalysts in conjunction with those aforementioned may be used, such as in various shapes; deposited in well known manner on carriers; cobalt, tin, vanadium, molybdenum, chromium, tungsten, or their compounds; promoted or not; in admixture if desired, with or without small amounts of acid, acids, halogen or derivatives of halogens; all sulphide catalysts of hydrogenating efficacy, in the form of shapes, pellets, extruded lengths, comminuted, with or without the presence of other materials possessing hydrogenating properties, or not; such as asbestos, quartz, earths, lumps of brick, etc.

As stated in the foregoing, step-wise conver- 51011, as opposed to total conversion in one pass through a reactor, comprises the process of the present invention, wherein tars or fractions thereof, are converted, substantially in entirety, into solvents having an aromaticity of in the order of 50%, or greater.

By the term superior solvency as used herein and in the appended claims is meant that the solvents of the present process are of greater solvency than hydrocarbon solvents commercially available, and have, among other things, an aromaticity of in the order of 50%, or greater.

When adjusting the sulphur content of the feed stock, including recycle material, so as to provide that hydrogen sulphide partial pressure necessary for maintenance of at least a portion of the catalyst in sulphide form, the sulphur may be added as elemental sulphur, or any form of sulphur capable of providing aforesaid requirement. Some of the feed stocks may, however, contain suificient sulphur without addition thereo.

At times when using as starting material certain tar fractions that contain a large percentage of molecular complexes, it may be desirable to at least partially depolymerize said molecular complexes by addition of a solvent thereto.

From the foregoing disclosure it will be seen ihat the present process provides a method for converting tar, or fractions thereof, into solvents, said conversion being characterized by subjecting said tar, and/or fractions thereof, while in liquid phase in the presence of a sulphide catalyst to the action of hydrogen and hydrogen sulphide with time, temperature and pressure so controlled as to produce solvent increment, and recovering from the beneficiated material a solvent having an aromaticity of in the order of 50% or greater.

Convenient methods for the evaluation of plasticizers or the like may be secured from chapter VI, page 96 et seq., of The Technology of Solvents by Otto Jordan, Mannheim, Germany, first English translation, by Alan D. Whitehead, Chemical Publishing Company of New York, Inc., New York, New York.

Minor changes may be made in the details of the foregoing without departing from the spirit, oi the invention.

1 claim:

In the production of plasticizers or the like, the process which comprises: subjecting a mixture of high temperature coal tar fractions boiling not in excess of about 15% at 355 C. to the action of hydrogen in the presence of a sulfide catalyst and hydrogen sulfide; carrying on the process for a period of about one and one-half hours, at a pressure in excess of about 200 atmospheres, and at a temperature selected between the limits of about 400-450 CL, whereby to induce plasticizing properties in the portion of the materials boiling between the limits of about 300-360 C.; and recovering from the beneficiated mass a substance of induced plasticizing properties boiling substantially between the temperatures last named.

JACQUELIN E. HARVEY, JR. 

